More specifically the subject of the invention is a DC motor of the type comprising a wound rotor with at least two pairs of poles, including a stack of laminations that defines an even number of slots, at least equal to 8, and associated with which are a commutator with an even number of segments and a closed distributed winding the wires of which extend in said slots and are connected in a predetermined manner to the segments of the commutator.
In prior art motors of this type, the winding of the rotor is typically of the lap type, or of the wave type.
The lap-type winding is generally preferred for low-voltage applications with high current intensities. This type of motor may be used, for example, as the motor of a radiator fan on a motor vehicle.
These types of motors entail the use of a large quantity of copper and of a high number of brushes and associated accessories in the brush-holder. Such a motor is therefore also relatively heavy.
Wave type windings have a limitation on the number of rotor teeth and commutator segments due to the winding sequence. The commutator pitch Yc must be equal to (C±1)/P where C is the number of segments and P is the number of pole pairs. For example, for a 4 pole motor having 18 segments, the equation gives Yc as (18±1)/2 or 17/2 or 19/2 which is not a whole number and thus can not be wound as a wave type winding.
However, a wave type winding can have certain benefits over a lap type winding in terms of weight and construction for motors with more than one pair of poles, e.g. 4 poles, 6 poles, 8 poles, etc.